Whats Up, Ron? is a monthly almanac for Northern American astronomersastras

WHAT'S UP?

by Ronald A. Leeseberg, the Star Geezer

February 2011 - Vol. 15 No. 2

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Features: Calendar | Lunar Almanac | Monthly Topic

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

Angular Measurement Review: It is interesting to note that the relationship between the angle subtended by combinations of fingers on your fully outstretched arm are the same for all viewers. This is due to the fact that the hand's size is proportional to the arm's length. A shorter arm is attached to a smaller hand while a longer arm is attached to a larger hand, thus the angle measured remains the same. If you hold your arm fully outstretched, your little finger, when sighted down your arm, is one degree wide. Your three middle fingers is five degrees, your fist, 10 degrees, and the distance between your little finger and your pointer finger is 15 degrees no matter what your age or size.

This Month's Night Sky - The stars of Orion appear highest in the S early in the evening. It's asterism reminds me of a slightly misshaped hourglass with three bright "belt" stars at the middle "pinch". The fuzzy patch of light below the middle belt star is M42, the Great Orion Nebula. Sirius (Canis Major), the brightest star in the night sky, Procyon (Canis Minor) and Betelgeuse (Orion) form an asterism known as the "Winter Triangle" which stands high in the S this month. Other prominent stars are: Rigel (also in Orion) and Aldebaran (Taurus) both in the SW. Castor and Pollux (Gemini "twins") are high overhead at 10 PM while Arcturus (Bootes) rises above the E horizon. The "Big Dipper" asterism (Ursa Major) now "stands" upright on its "handle" in the NE.

MERCURY rises in the SE only around 45 minutes before the Sun on the 1st. of the month. It may be visible, very low through the 4th. Beware the rising Sun! VENUS also rises in the SE about three hours before the Sun. By month's end, it will rise only 2 hours before Sunrise. MARS reaches conjunction (when the Earth and Mars are on oppopsite sides of the Sun) on the 4th. so will not be visible this month. JUPITER is in the SW sky by dusk and will set at around 9:30 at the beginning of the month. By month's end, it will set by 8:00. SATURN rises in the E at aronnd 10:30 at the beginning of the month however, by month's end, it rises aroun 8:30. It "moves" through the S night sky and is lost in the Sun's glare in the SW.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time.; Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times. Unfortunately some of these events may occur during daylight hours in your area.

DATE EVENT
01
At about 15 minutes before the Sun comes up, Mercury might be visible below a thin crescent Moon. The bright "star" to the upper left is the planet Venus. IF YOU ARE USING AN OPTICAL INSTRUMENT, BEWARE OF THE SUN!
06

Look W after Sunset to see a conjunction (6 degrees)of Jupiter and the crescentr Moon.

07
Look SW at 5 AM to see a conjunction (7 degrees) of the Moon and Jupiter.
19-Mar 3
Look W from a dark location, at about an hour after sunset, to view zodiacal light. ("Zodiacal light" is a vertical band of white light believed to be sunlight reflected from meteoriods found in the plane of the ecliptic, the apparent "path" of the Sun, Moon and Planets as they travel across our sky.) It will appear to be a very large, but very dim, pyramid of of white light, "leaning" to the left. Note Jupiter at its base.
21
Look SW, about a half hour+ before sunrise, to see a triangular pattern formed by the gibbous Moon (bottom), the bright star, Spica of Virgo (upper left) and Saturn (a bit higher, upper right). Note the four stars below the Moon. They remind me of a kite flying sideways. These are the bright stars of Corvus, the crow, and their appearance is a sure harbinger of spring!
25
At dawn, look SE to view a pseudo-conjunction of the reddish star, Antares (Scorpius) and the Moon. Antares is often mistaken for the planet Mars due to their similar reddish colors. Its name means "not Mars" (prefix "ant-" means against or not, and "ares", the Latin word meaning Mars.)
28
At dawn, look SE to see a conjunction of Venus and the Moon. Venus is now the "daystar".
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Lunar Almanac for February 2011

Phases of the Moon Phase and Date(s)

Best viewed before local midnight

New
02

Deep Space Objects

1st. Qtr
11

Planets & Moon

Full
18

Moon

Last
Qtr 24

Deep Space & Planets

Topic of the month: Sidewalk Astronomy, Telescope Types

Unfortunately, there is no perfect telescope for all occasion so let's begin with the basics:

The objective is the telescope's light gathering system. In a refractor it is a lens, usually consisting two or three elements, located at the front of the instrument. In the reflector, it is a mirror located at the rear of the telescope. Today's most popular telescopes are catadioptrics. also having a mirror in the rear and a corrector plate (lens) at its front. All optical instruments suffer, to varying degrees, from aberration. Portions of the image produced are out of focus. One type is chromatic and the other is spherical. Naturally there is usually a direct relationship between cost and the degree of the correction of these problems.

Every telescope has its own focal length. This is the distance from the objective (front lens or rear mirror) and its ocular or eyepiece. If the focal length is divided by the telescopes clear aperture (usually the objective's diameter, remembering that both the refractor and the catadioptric telescopes have secondary mirrors which effectively reduce their apertures.

If the focal length of the telescope is divided by its aperture (using common units, usually millimeters), its focal ratio (f/number) is determined. The f/number determines both degree of a telescope's magnification as well as it size of its visual field. Unfortunately it is an inverse relationship. The larger the f/number the greater the magnification but the smaller the field. Of course, the smaller the f/number, the larger the field.

For my street astronomy, I use refractors. My 2.4" solar telescope has an f/number of f/11 (660mm/60mm) and my 120" telescope has an f/number of f/8.3 (1000/120). Since, due to the usual intense street lighting, only very bright celestrial objects are visible through the haze, greater magnification of the Sun, Moon and the bright planets and bright, but compact, deep space objects is more appropriate. These smaller refractors are easier to set up and transport. Also, since they are sealed, dust is less of a problem, and they reach equalized temperature very quickly.

--See you next month!
Ron, the star geezer

This installment of "Whats Up?" is ©2011 Ronald A. Leeseberg, encoded by Dawn Jenkins for Astra's Stargate.

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